1. Field of the Invention
The invention relates in general to a method of fabricating a semiconductor device, and more particular, to a method of fabricating a memory device.
2. Description of Related Art
As image input, process and finishing have evoked public interest, the scanner is now the basic equipment for many computer users. The scanner is used to scan the text or graphic information of a document, a magazine, a book or a picture. The scanned information is then input to the computer for further process. Of the various kinds of scanners, the flatbed scanner is very common. The scan module of the flatbed scanner is installed under a transparent platform to scan the document disposed on the transparent platform by iterative movement. As the scan module itself does not have power, a driving mechanism such as a step motor, a gear and a belt is required. While scanning a document by the flatbed scanner, the document disposed on the transparent platform has to be covered with a cover lid, such that the document is appressed on the transparent platform for scan.
The conventional optical scan module (referring to FIG. 1) comprises a light source 100, a reflecting mirror set 400, an optical lens 500, an optical sensor 600 (such as a charged-couple device, CCD), and a main body 700. The light source 100, the reflecting mirror set 400, the optical lens 500 and the optical sensor 600 are located in the main body 700. The light source 100 radiates the document on the transparent platform 300 that is reflected to transmit an image light. The reflecting mirror set 400 includes multiple reflecting mirrors 401, 402 and 403 along the optical path of the image light, such that the image of the document 200 is directed into the reflecting mirror set 400. Being reflected from the reflecting mirror set 400, the image light is transmitted to the optical lens 500. Upon the reception, the optical lens 500 displays the image light of the document transmitted from the reflecting mirror set 400 to the charged-couple device 600.
As shown in FIG. 2, the mounting apparatus for the optical lens 500 is installed in the main body 700 and is integrally formed therewith. The mounting apparatus has a near trapezoid seat, of which a front end has a hollow lens thimble 800 for mounting the optical lens 500. That is, the optical lens 500 is telescopically received within the lens thimble 800. After adjusting the focal length, glue dispense or a screw is used to reinforce the fixture. The charged-couple device 600 is mounted at the rear side of the trapezoid seat of the mounting apparatus to receive the image light transmitted from the optical lens 500.
To comply with the trends of being light, thin, short and small, the scanner is formed with a shrinking and delicate dimension. The optical cone of the image light projected from the optical lens 500 to the charged-couple device 600 becomes smaller and smaller. As a result, the depth of focus becomes shallower and shallower. An accurate adjustment of the relative positions for the optical lens 500 and the charged-couple device becomes crucial for the correct depth of focus.
After the skew in the direction parallel to the base plate is adjusted, the base plate of the conventional charged-couple device 600 is directly locked to the main body (at the rear side of the trapezoid seat of the mounting apparatus of the optical lens) with a screw, so that the distance to the optical lens 500 cannot be further adjusted. Thus, the adjustment of the depth of focus between the optical lens 500 and the charged-couple device 600 can only be made at the optical lens 500. To allow the charged-couple device 600 to adjust the position (that is, the distance to the optical lens 500) to match the correct depth of focus, the previously adjusted skew is inevitably changed. Therefore, three degrees of freedom have to be considered causing great difficulty in adjustment of the charged-couple device.